1. Field of the Invention
The present invention relates to a femoral prosthesis, and more particularly, to a prosthesis design which provides an improved fit within the intramedullary canal of the femur.
2. Prior Art
It is well known that the shape of the femoral intramedullary canal is variable. Thus, when a prosthesis is implanted within the canal, it must be properly fitted. If the prosthesis bears on a particular area of cortical bone surrounding the canal, pain may be experienced by the recipient of the prosthesis. Additionally, the prosthesis may loosen as a result of rotation within canal or because of downward pressure resulting from the weight of the user.
The geometry of the femoral intramedullary canal is that it has an oval shape in its upper portion adjacent the location where the femoral head and neck have been removed. The major axis of the oval extends in the medial to lateral direction. However, approximately 4 to 6 inches below its upper end, the canal narrows, and it transitions to a configuration in which it is oval shaped, the oval's major axis extending in the anterior/posterior direction.
Conventional femoral prostheses neglect the geometrical characteristics of the intramedullary canal just described. More particularly, while they are configured to accommodate the canal's proximal geometry, they typically have distal portions which are circular in cross-section. Thus, proper fitting of such prostheses is achieved only at the proximal end of the canal. This results in less than complete stable fixation leading to the problems previously described.